The present invention relates generally to telephone switching systems, and in particular to detection of failures in emergency calls placed through the telephone network.
The public telephone network is equipped to handle certain emergency calls, which are typically initiated by dialing a special number dedicated for emergencies. For example, in the United States, 9-1-1 is dedicated for emergency calls. These calls are typically routed to a regional center of operators that handle the calls and initiate the dispatch of services needed to respond to the emergency. These services include, for example, police, fire and paramedics.
Emergency calls typically receive some special treatment in the telephone network. This treatment generally includes dedicated resources for handling the calls and specialized routing. The dedicated resources typically included lines, trunks and switching equipment.
Switching systems are known to monitor the integrity of the switching system and associated resources. However, this monitoring is done at a high level with respect to all calls traveling through the network. For example, switching systems typically monitor the number of reorders, that is, calls resulting in a fast busy. A threshold is set such that a certain number of reorders result in an alarm to indicate a possibility of error. Other limited monitoring scenarios exist, but these scenarios do not single out monitoring of emergency calls.
Unfortunately, the general monitoring of the integrity of a switching system does not adequately identify problems in emergency calls. Since emergency calls typically represent only a small percentage of all calls through a switching system, grossly monitoring all calls may not identify problems with the relatively small number of emergency calls. Indeed, it is possible that a problem with all emergency calls through a switching system may go undetected where the majority of non-emergency calls are successful. This problem is exasperated by the fact that emergency calls are often routed using dedicated resources. Thus, a problem with a dedicated resource may cause all emergency calls to fail, while non-emergency calls, which do not rely on the faulty dedicated resource are completed without error. As an example, it is possible that through some fault, all emergency trunks on a switching system are out of service, while other resources are available. Nonetheless, system integrity monitoring may not alert an operator because the total failure of all emergency calls may not result in an error threshold sufficient to assert an alarm. Of course, this is not desirable due to the potential importance of any single emergency call.
Therefore, a need exists for a method and apparatus for monitoring emergency calls in a telephone network to facilitate higher reliability in emergency calls.
In accordance with one aspect the present invention, a method is provided for monitoring emergency calls in a telephone switching system. Upon receiving a call the sequence of called digits is detected. The detected sequence of digits is examined or compared with a predetermined sequence to determine if the call is an emergency call. For example, a sequence of 911 is detected in the United States to designate emergency calls. After detecting a sequence of digits, a further determination is made as to whether the call is an emergency call. This entails examining the call type to determine if the call type is designated an emergency call. If the call is an emergency call, as determined by the dialed digits or the call type, the call is monitored to determine if the call is completed successfully. If the call is not completed successfully or encounters errors, then an alarm is generated. The method is preferably applied across all switching systems in the telephone network that handle emergency calls, thereby insuring monitoring of emergency calls from end-to-end.
In another aspect of the present invention an apparatus is provided for monitoring emergency calls. The apparatus includes a line/trunk interface unit that interfaces telephone lines and/or trunks into a telephone switching system. The line/trunk interface unit receives a telephone call. A call digit processor is coupled to the line/trunk interface unit to detect the called digits associated with the call to determine if the called digits are a predetermined sequence indicating an emergency call. A call monitor is coupled to the call digit processor to monitor the calls determined to be emergency calls. If errors occur during the processing of the emergency calls, then the call monitor provides an indication of the error and an alarm is asserted.